In a paper machine environment, in order to measure a force, for example, a linear load, the pressure is usually measured. Pressure transmitters or detectors act as feedback members of force regulation circuits. In present-day lines of manufacture of paper, there are, on the average, about 500 points at which the pressure is measured.
Pressure detectors and regulation electronics of regulation valves always involve a certain extent of creep, as a result of which their regulation values may change in the course of time. For this reason, such regulation values should be checked at regular intervals. Since the number of points to be checked is high, it is desirable to make checking of the regulation pressures of regulation valves automatic in order that the pressure of each pressure transmitter or detector should not have to be checked separately manually.
In the prior art, calibration of the pressure detectors of regulation valves is carried out manually so that all pressure detectors of regulation valves at an object to be regulated are calibrated at regular intervals. In such a case, it has been necessary to carry out an abundance of unnecessary work, because calibration has not been necessary for some of the pressure detectors of the regulation valves. Since the amount of work used for manual calibration is considerable in the case of a large number of valves, calibration has been carried out relatively seldom, in which case, some of the pressure detectors of regulation valves may already have crept to a relatively great extent. Those pressure detectors of regulation valves that have crept pass either an excessively high or an excessively low pressure to the object to be regulated, which is, of course, an undesirable situation.
There are also applications in which the pressure transmitter that acts as the feedback member of the regulation circuit has been doubled, in which case, one pressure transmitter operates as a reference transmitter. In monitoring that has been carried into effect in this way, it is, however, not known which pressure transmitter shows the correct reading. In such an application, the condition of the reference transmitter should always be known.